1. Field of the Invention
The present invention relates to input devices for operating electric units, such as in-vehicle electric units, by rotating an operating member. In particular, the present invention relates to a force-feedback input device that applies torque to the operating member in an amount corresponding to the rotational angle of the operating member so that a certain operational feel, namely, force feedback, is imparted to an operator via the operating member.
2. Description of the Related Art
A typical force-feedback input device is generally provided with a rotatable knob disposed in a housing; a rotary encoder for detecting the rotational angle of the knob; a motor, which is capable of applying torque to the knob; and a controller, which controls the motor and also outputs a command signal to an electric unit subject to operation, based on the rotational angle of the knob detected by the rotary encoder.
Such a force-feedback input device is intended for outputting a command signal to an electric unit such as an in-vehicle electric unit, and this output of a command signal is implemented by rotating the knob. For example, such a force-feedback input device can be used for an airflow adjustment or a nozzle control of an in-vehicle air conditioner, for volume control or tuning control in a radio unit, and for volume control or tone control in an audio unit.
For example, for adjusting the airflow of an in-vehicle air conditioner, when the knob is rotated in a direction for raising the airflow level, the motor applies torque to the knob in a direction opposite to the rotation of the knob. Moreover, as the rotational angle of the knob rotating in the airflow-increasing direction increases, the torque applied in the opposite direction also increases. Accordingly, an operator is able to sense how much he/she has rotated the knob in the airflow-increasing direction from an operational feel (force feedback) produced by the increasing resistive force imparted to the knob.
In addition to a force-feedback input device of this type that imparts an operational feel to an operator with resistive force, there are other types of force-feedback input devices. One of the types, for example, applies torque in the same direction as the rotation of the knob to impart an accelerative force as an operational feel. Another type inverts the direction of the torque applied to the knob when the rotational angle of the knob exceeds a predetermined angle so as to impart a feel of a “click” to the operator.
Japanese Unexamined Patent Application Publication No. 2003-50639 discloses an example of a force-feedback input device.
There are problems in the conventional force-feedback input devices in view of size reduction. For manipulating the knob (operating member) in the conventional force-feedback input devices, the knob is held with two or more fingers, and this allows a great operating force to be applied to the knob. To generate an operational feel with, for example, resistive force in a state where such a great operating force is applied to the knob, a motor that is capable of outputting torque that corresponds to the operating force is required. This implies that a motor with a large dimension is required. In other words, the necessity of a large motor in the conventional force-feedback input devices is one of the reasons that causes difficulty in view of size reduction.